The invention relates to a pneumatically or electromechanically actuated disc brake having a brake caliper straddling a brake disc, a brake application device arranged in the brake caliper and comprising a rotary brake lever, at least one adjusting spindle, which is axially moveable by way of the brake application device, and an adjusting device, which is actuated by the brake lever and positioned in the brake caliper, and which serves, via an axial adjustment of the adjusting spindle, substantially to compensate for a wear-induced variation of the lift clearance between a brake pad and the brake disc.
Such a disc brake is disclosed, for example, by DE 94 22 342 U1, and by DE 10 2004 037 771 A1. Each of these documents shows and describes an adjusting device for a pneumatically actuated disc brake, in particular one of a sliding caliper design, which can also be used, however, in pneumatically actuated fixed or hinged caliper disc brakes.
Such an adjusting device serves to perform an automatic wear adjustment, so that the so-called “lift clearance,” by which is meant the gap between the brake pads and the brake disc in the non-actuated state, is kept constant irrespective of the state of wear and the wear pattern of the brake pads.
In the known disc brakes, adjusters, one of which is driven by a brake lever via a drive element, are arranged in the adjusting spindles in the form of threaded tubes. The drive element comprises two shifting pins, which engage in a shift fork of the adjuster of the adjusting spindle.
In a braking sequence, the brake lever coupled to a piston rod of a brake cylinder performs a pivoting or rotating movement, which after overcoming a so-called idle travel turns the adjuster and thereby the adjusting spindle. The brake lever hitherto used is manufactured by forging, the shifting pins being forged on in the process.
However, the known design has a number of quite serious disadvantageous. For example, a constant transmission over the entire pivoting range of the brake lever is not possible. Furthermore, due to the given tolerances, the play in the adjusting spindle drive, which at the same time represents the lift clearance between the brake disc and the brake pads, can only be adjusted very imprecisely.
Moreover, such a forging of the brake lever is considerably more complicated and, hence, more expensive to manufacture than a casting, it having so far proved impossible to form the known brake lever as a casting, owing to the configuration of the connected shifting pins, particularly in view of the required strength and the overall space available.
The object of the invention is to further develop a disc brake of the above-mentioned type, so as to improve its functionality and to allow more cost-effective manufacturing.
This object is achieved by a disc brake having a brake caliper straddling a brake disc, a brake application device arranged in the brake caliper and comprising a rotary brake lever, at least one adjusting spindle, which is axially moveable by way of the brake application device, and an adjusting device, which is actuated by the brake lever and positioned in the brake caliper, and which serves, via an axial adjustment of the adjusting spindle, substantially to compensate for a wear-induced variation of the lift clearance between a brake pad and the brake disc. The adjusting device includes a spur gear segment, which extends in the pivoting direction and is arranged on the brake lever, and which for adjustment purposes engages with a crown wheel operatively connected to the adjusting spindle.
The spur gear segment/crown wheel pairing is virtually free of play and produces a constant transmission over the entire pivoting range of the lever. The adjustment behavior of the entire brake is thereby considerably improved. The adjusting spindle is driven more precisely, which results in a more accurate adjustment of the lift clearance. This is preferably achieved by way of a shifting link in the adjusting spindle.
In addition, the invention allows the brake lever to be manufactured by casting, the spur gear segment, which extends in the pivoting direction of the brake lever, being cast on. Moreover, the brake lever can largely be used without intricate machining, at least in terms of the formed-on spur gear segment.
According to an advantageous development of the invention, the crown wheel is rotationally fixed on a central drive spindle, which is arranged between two adjusting spindles and which is connected to the adjusting spindles by way of a shifting link, that is to say a transmission mechanism.
Forming the brake lever as a casting with an integral spur gear segment allows it to be designed, for the same load-bearing capacity, with dimensions no greater than the hitherto forged-on shift fingers, so that it is possible to optimize the disc brake in terms of the functionality of the adjusting device, whilst retaining or possibly even reducing the current overall size.
The manufacturing costs of the brake lever, however, are much less than the existing forged brake lever. Significant advantages also accrue, in particular, in as much as disc brakes are used in large quantities.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.